Pneumatic tire

ABSTRACT

A pneumatic tire includes a tread portion provided with a pair of shoulder main grooves adjacent to each tread edge, and shoulder lateral grooves extending from each shoulder main grooves to each tread edge. Each shoulder lateral groove includes an axially inner portion extending from the shoulder main groove with a first angle, an axially middle portion extending from the axially inner portion with a second angle larger than the first angle, and an axially outer portion extending from the axially middle portion with a third angle smaller than the second angle. The shoulder lateral grooves include first and second shoulder lateral grooves alternately arranged in a circumferential direction of the tire. The axially middle portion of the first shoulder lateral groove is disposed axially inwardly of the axially middle portion of the second shoulder lateral groove.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a pneumatic tire, and in particular,relates to a pneumatic tire used for traveling on muddy roads.

Description of the Related Art

All-season tires for use on dry and muddy roads usually include a treadportion having a block pattern with a plurality of blocks dividedbetween circumferential main grooves and lateral grooves, foe example.Conventionally, in order to improve muddy road performance of suchtires, it is proposed increasing volume of lateral grooves forgenerating large traction on muddy roads by offering large mud shearingforce.

The tire having lateral grooves having large groove volume, however,tends to have disadvantage with respect to noise performance on dryroads. For example, pipe resonance noise is often generated in the maingrooves during traveling straight ahead on dry roads, and then it tendsto easily spread outside the tire from the tread edges through lateralgrooves.

Japanese unexamined Patent Application Publication No. 2012-218652discloses an all-season tire that is expected to have a superior noiseperformance as well as muddy road performance.

However, such a tire disclosed above has room for improving noiseperformance on dry roads.

SUMMARY OF THE INVENTION

The present invention has been worked out in light of the circumstancesdescribed above, and has a main object of providing a pneumatic tirehaving an improved muddy road performance while maintaining noiseperformance.

According to one aspect of the present invention, there is provided apneumatic tire including a tread portion having a pair of tread edges,the tread portion being provided with a pair of circumferentially andcontinuously extending shoulder main grooves adjacent to each tread edgeand a plurality of shoulder lateral grooves each extending axiallyoutwardly of the tire from each shoulder main groove to each tread edge.Each shoulder lateral groove includes an axially inner portion extendingfrom the shoulder main groove having a first angle with respect to anaxial direction of the tire, an axially middle portion extending fromthe axially inner portion having a second angle with respect to theaxial direction of the tire larger than the first angle of the axiallyinner portion, and an axially outer portion extending from the axiallymiddle portion having a third angle with respect to the axial directionof the tire smaller than the second angle of the axially middle portion.The shoulder lateral grooves include a first shoulder lateral groove anda second shoulder lateral groove which are alternately arranged in acircumferential direction of the tire. The axially middle portion of thefirst shoulder lateral groove is disposed axially inwardly of theaxially middle portion of the second shoulder lateral groove.

In the first aspect of the present invention, the axially outer portionof the shoulder lateral groove may have a groove width increasing towardaxially outwardly of the tire.

In the first aspect of the present invention, the third angle of thesecond shoulder lateral groove may be smaller than the third angle ofthe first shoulder lateral groove.

In the first aspect of the present invention, the axially middle portionof the second shoulder lateral groove may have a circumferential lengthlarger than that of the axially middle portion of the first shoulderlateral groove.

In the first aspect of the present invention, the tread portion maycomprise a shoulder block row that includes a plurality of shoulderblocks divided by the shoulder lateral grooves between the tread edgeand the shoulder main groove. At least one shoulder block may bedisposed a circumferentially extending longitudinal sipe thatcommunicates between circumferentially adjacent shoulder lateralgrooves.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a development view of a tread portion of a pneumatic tireaccording to an embodiment of the present invention;

FIGS. 2A and 2B are respective partial enlarged views of a shoulder maingroove and a center main groove of FIG. 1;

FIGS. 3 and 4 are partial enlarged views of shoulder portions in theright side of the tread portion of FIG. 1;

FIG. 5 is a partial enlarged view of a middle portion in the right sideof the tread portion of FIG. 1;

FIG. 6 is a development view of the tread portion according to anotherembodiment of the present invention; and

FIGS. 7 and 8 are development views of the tread portion according tocomparative example of the present invention.

DESCRIPTION OF THE EMBODIMENTS

An embodiment of the present invention will be explained below withreference to the accompanying drawings.

FIG. 1 illustrates a pneumatic tire 1 in accordance with the presentembodiment that may be suitably embodied as an all-season tire forfour-wheel drive vehicles.

The tire 1 includes a tread portion 2 having a pair of tread edges Te,Te. The tread portion 2 is provided with a pair of circumferentially andcontinuously extending shoulder main grooves 3, 3 adjacent to each treadedge Te and a pair of circumferentially and continuously extendingcenter main grooves 4, 4 disposed axially inwardly of the shoulder maingrooves 3, 3. Thus, the tread portion 2 is separated into a plurality ofland portions that include a pair of shoulder portions 5 each of whichis between adjacent shoulder main groove 3 and the tread edge Te, a pairof middle portions 6 each of which is between adjacent shoulder maingroove 3 and center groove 4, and a center portion 7 between center maingrooves 4, 4.

Here, tread edges Te are the axial outermost edges of the groundcontacting patch of the tread portion 2 which occurs under a normallyinflated loaded condition when the camber angle of the tire is zero. Thenormally inflated loaded condition is such that the tire is mounted on astandard wheel rim and inflated to a standard pressure and loaded with astandard tire load.

The tread width TW of the tread portion 2 is defined as the widthmeasured under a normally inflated unloaded condition, as the axialdistance between the tread edges Te, Te determined as above.

The normally inflated unloaded condition is such that the tire ismounted on the standard wheel rim and is inflated to the standardpressure but loaded with no tire load. In this application includingspecification and claims, various dimensions, positions and the like ofthe tire refer to those under the normally inflated unloaded conditionof the tire unless otherwise noted.

The standard wheel rim is a wheel rim officially approved or recommendedfor the tire by standards organizations, i.e. JATMA, TRA, ETRTO, and thelike which are effective in the area where the tire is manufactured,sold or used. For example, the standard wheel rim is the “standard rim”specified in JATMA, the “Measuring Rim” in ETRTO, and the “Design Rim”in TRA or the like.

The standard pressure and the standard tire load are the maximum airpressure and the maximum tire load for the tire specified by the sameorganization in the Air-pressure/Maximum-load Table or similar list. Thestandard pressure is the “maximum air pressure” in JATMA, the “InflationPressure” in ETRTO, and the maximum pressure given in the “Tire LoadLimits at Various Cold Inflation Pressures” table in TRA or the like.

The standard tire load is the “maximum load capacity” in JATMA, the“Load Capacity” in ETRTO, and the maximum value given in theabove-mentioned table in TRA or the like.

In case of passenger car tires, however, the standard pressure andstandard tire load are uniformly defined by 180 kPa and 88% of themaximum tire load, respectively.

FIG. 2A illustrates the shoulder main groove 3 in the left side of FIG.1, and FIG. 2B illustrates the center main groove 4 in the left side ofFIG. 1. As shown in FIGS. 2A and 2B, each of the shoulder main groove 3and the center main groove 4 extends in a trapezoid wave manner thatincludes a plurality of circumferentially extending axially outer parts10, a plurality of circumferentially extending axially inner parts 11disposed axially inwardly of the axially outer parts 10, and a pluralityof inclined parts 12 connecting between the axially outer part 10 andthe axially inner part 11. The axially outer parts 10 and the axiallyinner parts 11 may improve self-cleaning feature for the tread portion 2that easily remove mud therefrom during traveling on muddy roads. Theinclined parts 12 include first inclined parts 12A that are inclined ata first direction (downward to the right in this embodiment), and secondinclined parts 12B that are inclined at a second direction (upward tothe right in this embodiment) opposite to the first direction. Sincesuch inclined parts 12 include lateral edge components, the inclinedparts 12 may effectively bite loose muddy road surface, and firmlycompresses it and shears for generating large mud shearing force. Theshoulder main grooves 3 and the center main grooves 4, however, areparticularly not limited the embodiment above.

In order to improve muddy road performance and noise performance inproper balance, the respective groove widths W1, W2 measured at theaxially inner or outer parts of the shoulder main grooves 3 and thecenter main grooves 4 are preferably in a range of from 1.0% to 4.0% inrelation to the tread width TW. Furthermore, groove depths of theshoulder main grooves 3 and the center main grooves 4 are preferably ina range of from 8.0 to 12.0 mm.

Referring back to FIG. 1, regarding the location for shoulder maingroove 3, the axial distance L1 between the tire equator C and theamplitude centerline G3 of the shoulder main groove 3 is preferably in arange of from 15% to 35% in relation to the tread width TW. Regardingthe location for center main groove 4, the axial distance L2 between thetire equator c and the amplitude centerline G4 of the center main groove4 is preferably in a range of from 4% to 9% in relation to the treadwidth TW. Thus, mud is effectively removed from under the tread portion2 during traveling so that muddy road performance may further beimproved.

The shoulder portion 5 is provided with a plurality of shoulder lateralgrooves 8 that extend beyond the tread edge Te from the shoulder maingroove 3 to form a shoulder block row 9R including a plurality ofshoulder blocks 9.

FIG. 3 illustrates a partial enlarged view of the shoulder portion 5 inthe right side of the tread portion 2 of FIG. 1. As shown in FIG. 3,each shoulder lateral groove 8 includes an axially inner portion 16extending from the shoulder main groove 3 having a first angle θ1 withrespect to the axial direction of the tire, an axially middle portion 17extending from the axially inner portion 16 having a second angle θ2with respect to the axial direction of the tire larger than the firstangle θ1 of the axially inner portion 16, and an axially outer portion18 extending from the axially middle portion 17 to the tread edge Tewith a third angle θ3 with respect to the axial direction of the tiresmaller than the second angle θ2 of the axially middle portion 17. Theaxially inner portion 16 and the axially outer portion 18 may generatelarge mud shearing force while pushing mud therein out from the treadedge Te for improving self-cleaning feature for the tread portion 2. Theaxially middle portion 17 may disturb the air flow with pipe resonancevibration that passes from the shoulder main groove 3 to the tread edgeTe so that noise performance may further be improved.

In this embodiment, each of axially inner, middle and outer portions 16,17 and 18 is respectively inclined at the same direction so as tosmoothly push mud out of the tread edge Te.

The shoulder lateral grooves 8 include a plurality of first shoulderlateral grooves 14, and a plurality of second shoulder lateral grooves15, wherein the first shoulder lateral groove 14 and the second shoulderlateral groove 15 are alternately arranged in the circumferentialdirection of the tire.

The axially middle portion 17 of the first shoulder lateral groove 14 isdisposed axially inwardly of the axially middle portion 17 of the secondshoulder lateral groove 15. Thus, since each shoulder block 9 hasirregular rigidity along with the axial direction of the tire, it tendsto vibrate with relatively large amplitude during traveling so that mudin the shoulder lateral groove 8 is easily removed therefrom.

Here, the location of the axially middle portion 17 of the shoulderlateral groove 8 is defined as an axially innermost point 13 a on eithergroove edges 8 a of the middle portion 17. In this embodiment of FIG. 3,the axially innermost point 13 a is defined on the below groove edge 8 aof the shoulder lateral groove 8. Furthermore, in the event that theaxially inner portion 16 and the axially middle portion 17 are smoothlyconnected using a chamfered arc, the axially innermost point 13 amentioned above is defined as a center point on the chamfered arc.

Regarding the arrangement of first and second shoulder lateral grooves14, 15, the axial length La between the axially inner most points 13 aof first and second shoulder lateral grooves 14, 15 is preferably in arange of from 15% to 25% in relation to the maximum axial width ws ofthe shoulder block 9, in order to further improve the advantage above.

In order to further improve the advantage above, the axially outmostpoint 13 b of the axially middle portion 17 of the first shoulderlateral groove 14 is preferably disposed axially outwardly of theaxially innermost point 13 a of the axially middle portion 17 of thesecond shoulder lateral groove 15.

FIG. 4 also illustrates a partial enlarged view of the shoulder portion5 in the right side of the tread portion 2 of FIG. 1. As shown in FIG.4, the axially middle portion 17 of the second shoulder lateral groove15 preferably has the circumferential length L4 larger than thecircumferential length L3 of the axially middle portion 17 of the firstshoulder lateral groove 14. Thus, the shoulder block 9 may be configuredto have more preferable irregular rigidity along with the axialdirection of the tire for improving self-cleaning feature for the treadportion 2 as mentioned above. In order to further improve muddy roadperformance as well as noise performance, the circumferential length L4of the axially middle portion 17 of the second shoulder lateral groove15 is preferably in a range of from 1.1 to 1.5 times in relation to thecircumferential length L3 of the axially middle portion 17 of the firstshoulder lateral groove 14.

In the same point of view above, the circumferential length L3 of theaxially middle portion 17 of the first shoulder lateral groove 14 ispreferably in a range of from 10% to 22% in relation to thecircumferential maximum length Ls of the shoulder block 9.

The axially outer portion 18 of the shoulder lateral groove 8 has agroove width W4 measured along with the circumferential direction of thetire that is gradually increasing toward the tread edge Te. Thus,self-cleaning feature for the shoulder lateral groove 8 mentioned abovemay further be improved, especially during cornering. In order tofurther improve muddy road performance with self-cleaning feature forthe tread portion 2 while maintaining an improved noise performance, thegroove width W4 a at the tread edge Te of the axially outer portion 18is preferably in a range of from 1.10 to 1.35 times in relation to thegroove width W4 b at the axially innermost of the axially outer portion18. In the same point of view above, the groove width W4 of the axiallyouter portion 18 is preferably in a range of from 10% to 30% in relationto the circumferential maximum length Ls of the shoulder block 9.

In this embodiment, the axially middle portion 17 also has the groovewidth W5 measured along with the circumferential direction of the tirethat is gradually increasing toward the tread edge Te for furtherimproving self-cleaning feature for the tread portion 2 above.

Although it is not particularly limited, the axially inner portion 16 ofthe shoulder lateral groove 8 preferably has the circumferential groovewidth W6 in a range of from 2.0% to 7.0% in relation to thecircumferential maximum length Ls of the shoulder block 9 so as toeffectively disturb the air flow with pipe resonance vibration thatpasses from the shoulder main groove 3 thereto.

Referring back to FIG. 3, the third angle θ3 b of the axially outerportion 18 of the second shoulder lateral groove 15 is preferablysmaller than the third angle θ3 a of the axially outer portion 18 of thefirst shoulder lateral groove 14. Thus, circumferential rigidity of theshoulder block 9 between the adjacent axially outer portions 18, 18tends to decrease toward the tread edge Te, whereby self-cleaningfeature for the tread portion 2 on the shoulder lateral groove 8 isfurther improved. In order to further improve the advantage above, thethird angle θ3 b of the axially outer portion 18 of the second shoulderlateral groove 15 is preferably in a range of from 5 to 25 degrees withrespect to the axial direction of the tire. Furthermore, the differenceθ3 a−θ3 b between the third angles θ3 a−θ3 b is preferably in a range offrom 5 to 15 degrees.

In order to further improve muddy road performance as well as noiseperformance, the first angle θ1 of the axially inner portion 16 ispreferably in a range of from 15 to 35 degrees. Similarly, the secondangle θ2 of the axially middle portion 17 is preferably in a range offrom 40 to 60 degrees.

Referring back to FIG. 1, the circumferential length Lb1 of the firstshoulder lateral groove 14 is preferably in a range of from 0.9 to 1.1times in relation to the circumferential length Lb2 of the secondshoulder lateral groove 15. Thus, self-cleaning feature for treadportion 2 and disturbing for pipe resonance noise in the first andsecond shoulder lateral grooves 14 and 15 is further improved.

In this embodiment, each shoulder lateral groove 8 is communicated withthe shoulder main groove at its outer part 10 including the corner pointbetween the inclined part 12 and the outer part 10 so that the inclinedpart 12 and the axially inner portion 16 are smoothly connected eachother. Thus, mud in the shoulder main groove 3 is smoothly pushed intoeach axially inner portion 16 of the shoulder lateral groove 8, due to acontact pressure during traveling. Furthermore, the inclined part 12 andthe axially inner portion 16 may generate large mud shearing force byshearing an axially long compressed mud formed therein so that muddyroad performance is further improved.

In order to effectively prevent pipe noise resonance transmitted intothe shoulder lateral groove 8 from the shoulder main groove 3, theaxially inner portion 16 of the shoulder lateral groove 8 preferably hasits groove depth (not shown) in a range of from 40% to 60% in relationto the groove depth of the shoulder main groove 3. In order to furthergenerate large mud shearing force, the axially outer portion 18 of theshoulder lateral groove 8 preferably has its groove depth in a range offrom 75% to 95% in relation to the groove depth of the shoulder maingroove 3. The axially middle portion 17 of the shoulder lateral groove 8preferably has its groove depth increasing from the axially innerportion 16 to the axially outer portion 18.

As shown in FIG. 4, the shoulder block 9 is disposed a circumferentiallyextending longitudinal sipe 20, an axially inner sipe 21 disposedaxially inwardly of the longitudinal sipe 20, and an axially outer sipe22 disposed axially outwardly of the longitudinal sipe 20. Thus, sincethese sipes 20, 21 and 22 make the shoulder block soften in well balancemanner, the shoulder block 9 further vibrates during traveling, wherebyself-cleaning feature for the tread portion 2 may further be improved.

Here, a sipe is defined as a thin slit or the like, having a width ofless than 2 mm.

The longitudinal sipe 20 is a full-opened sipe having its both ends eachof which communicates with the other groove. The longitudinal sipe 20 ispreferably disposed in a center region having the axial width of 20% inrelation to the axial maximum width Ws of the shoulder block 9.

The axially inner sipe 21 is a semi-opened sipe that has its one endcommunicated with the shoulder main groove 3 and its other endterminating within the shoulder block without reaching the other grooveor sipe. The axially inner sipe 21 makes the shoulder block soften atits axially inner part. Thus, the axially inner part of the shoulderblock 9 tends to vibrate with large during traveling so that mud cloggedin the shoulder lateral groove 3 is effectively removed therefrom. Inorder to further improve the advantage above, the axially inner andouter sipes 21 and 22 have the same inclination with the shoulderlateral groove 8.

The longitudinal sipe 20, axially inner sipe 21 and axially outer sipe22 preferably have the respective widths in a range of from 0.6 to 1.0mm. The longitudinal sipe 20, axially inner sipe 21 and axially outersipe 22 preferably have the respective depths in a range of from 50% to75% in relation to the groove depth of the axially outer portion 18 ofthe shoulder lateral groove 8.

FIG. 5 illustrates a partial enlarged view of the middle portion 6 inthe right side of the tread portion 2 of FIG. 1. Referring to FIG. 5,the middle portion 6 is provided with a plurality of outer middle luggrooves 24, a plurality of inner middle lug grooves 25, and a pluralityof longitudinal sub grooves 26.

Each outer middle lug groove 24 extends from the shoulder main groove 3to its axially inner end that terminates within the middle portion 6.Each inner middle lug groove 25 extends from the center main groove 4 toits axially outer end that terminates within the middle portion 6.

The longitudinal sub grooves 26 include first longitudinal sub grooves26 a and second longitudinal sub grooves 26 b. Each first longitudinalsub groove 26 a connects between the outer middle lug groove 24 and theinner middle lug groove 25. Each second longitudinal sub groove 26 bconnects between adjacent outer middle lug grooves 24. Thus, the middleportion 6 is divided into a block row that includes a first outer block6 a, a second outer block 6 b, and an inner block 6 c.

The first outer block 6 a is defined among the shoulder main groove 3,outer middle lug grooves 24, the inner middle lug groove 25, and thefirst sub longitudinal grooves 26 a. The second outer block 6 b isdefined among the shoulder main groove 3, outer middle lug grooves 24,and the second sub longitudinal groove 26 b. The inner block 6 c isdefined among the center main groove 4, outer middle lug grooves 24,inner middle lug grooves 25, the second sub longitudinal groove 26 b,and the first sub longitudinal grooves 26 a. Since the middle portion 6configured to the above tends to have low rigidity, mud in the outermiddle lug grooves 24 and inner middle lug grooves 25 is easily removedtherefrom.

The outer middle lug grooves 24 have groove widths W8 measured along thecircumferential direction of the tire increasing toward the shouldermain groove 3. The inner middle lug grooves 25 have groove widths W9measured along the circumferential direction of the tire increasingtoward the center main groove 4.

Each of the inner blocks 6 c is provided with a first semi-opened middlesipe 29A that straightly extends and is inclined at one direction(upward to the right in this embodiment) with respect to the axialdirection of the tire. The first semi-opened middle sipe 29A extendsfrom the center main groove 4 to its axially outer end that terminateswithin the middle portion 6.

Each of the first outer blocks 6 a and the second blocks 6 b is providedwith a second semi-opened sipe 29B that straightly extends and isinclined at one direction (upward to the right in this embodiment) withrespect to the axial direction of the tire. The second semi-openedmiddle sipe 29B extends from the shoulder main groove 3 to its axiallyinner end that terminates within the middle portion 6. These semi-openedsipes 29A, 29B may adjust rigidity of the middle portion 6 on itsaxially both sides so that each mud in the outer middle lug grooves 24,inner middle lug grooves 25, shoulder main groove 4 and center maingroove 3 is further easily removed therefrom.

Referring back to FIG. 1, the center portion 7 is provided with a centerlug groove 31 and a center sipe 32. Each of the center lug groove 31 andthe center sipe 32 extends from the center main groove 4 to its axiallyinner end that terminates without reaching the tire equator C. Since thecenter portion 7 is configured to have low rigidity at the axially bothends, the center portion 7 may give vibration to mud clogged in thecenter main groove 4 so as to easily be removed it from there duringtraveling.

The present invention is more specifically described and explained bymeans of the following Examples and References. It is to be understoodthat the present invention is not limited to these Examples andembodiments described above.

Comparison Test

In order to confirm the advantage of the invention, pneumatic tireshaving a tire size of 285/60R18 with basic tread patterns of FIG. 1except for details shown in Table 1 were made and tested. Major commonspecifics of tires and test method are as follows.

Details of Test Tires:

Rim size: 18×8.0 J

Internal pressure: 230 kPa

Tread width TW: 224 mm

Shoulder main groove depth: 10.0 mm

Center main groove depth: 10.0 mm

Axially inner portion of the shoulder lateral groove depth: 4.5 mm

Axially outer portion of the shoulder lateral groove depth: 9.0 mm

Axially middle portion of the shoulder lateral groove depth: 4.5 to 9.0mm (gradually increasing toward the axially outer portion)

Outer and inner lug groove depths: 8.0 mm

Center lug groove depth: 5.0 mm

Ratio of each sipe depth to shoulder main groove depth: 30% to 80%

Noise Performance Test:

A four-wheel drive car with a displacement of 4,600 cc provided withtest tires as four wheels was driven at a speed of 50 km/h on a roadnoise measurement test course having rough asphalt surface, and theinternal vehicle noise was measured with a microphone set at thedriver's right ear position. Based on the noise measured above, the peaksound level of the pipe resonance noise ranging about 240 Hz wasanalyzed. The results are indicated the reciprocal number of the peaksound level in Table 1 by an index based on Ref.1 being 100. The largerthe index number, the better the noise performance is.

Muddy Road Performance Test:

The test vehicle above was driven by a professional test driver on loosemuddy road, and evaluated traction force when starting and acceleratingof each test tire according to his feeling. The results are shown with ascore of 100 representing a value in Ref.1. The larger the value, thebetter the performance is.

Test results are shown in Table 1.

TABLE 1 Ref. 1 Ref. 2 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Ex. 8Tread pattern FIG. 7 FIG. 8 FIG. 1 FIG. 1 FIG. 1 FIG. 1 FIG. 1 FIG. 1FIG. 1 FIG. 1 Ratio La/Ws (%) 20 — 20 10 15 25 30 20 20 20 Ratio W4a/W4b1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.05 1.1 1.35 θ3a-θ3b (deg.) 10 10 10 10 1010 10 10 10 10 Ratio L4/L3 1.3 1.3 1.3 1.3 1.3 1.3 1.3 1.3 1.3 1.3 Muddyroad performance [Score] 100 102 115 105 110 110 105 100 105 120 Noiseperformance [Index] 100 100 100 100 100 100 100 110 105 90 Ex. 9 Ex. 10Ex. 11 Ex. 12 Ex. 13 Ex. 14 Ex. 15 Ex. 16 Ex. 17 Ex. 18 Tread patternFIG. 1 FIG. 1 FIG. 1 FIG. 1 FIG. 1 FIG. 1 FIG. 1 FIG. 1 FIG. 1 FIG. 6Ratio La/Ws (%) 20 20 20 20 20 20 20 20 20 20 Ratio W4a/W4b 1.4 1.2 1.21.2 1.2 1.2 1.2 1.2 1.2 1.2 θ3a-θ3b (deg.) 10 2 5 15 20 10 10 10 10 10Ratio L4/L3 1.3 1.3 1.3 1.3 1.3 1 1.1 1.5 1.6 1.3 Muddy road performance[Score] 125 105 110 110 105 105 110 110 105 105 Noise performance[Index] 85 100 100 100 100 100 100 100 100 100

From the test results, it was confirmed that Example tires in accordancewith the present embodiment of the invention can be effectively improvedmuddy road performance while maintaining noise performance. Through theother experiments used tires having the different size, the same resultsas mentioned above was confirmed.

What is claimed is:
 1. A pneumatic tire comprising: a tread portionhaving a pair of tread edges, the tread portion being provided with apair of circumferentially and continuously extending shoulder maingrooves adjacent to each tread edge and a plurality of shoulder lateralgrooves each extending axially outwardly of the tire from each shouldermain groove to each tread edge, each shoulder lateral groove comprising:an axially inner portion extending from the shoulder main groove havinga first angle with respect to an axial direction of the tire; an axiallymiddle portion extending from the axially inner portion having a secondangle with respect to the axial direction of the tire larger than thefirst angle of the axially inner portion, wherein the second angle is ina range of from 40 to 60 degrees; and an axially outer portion extendingfrom the axially middle portion having a third angle with respect to theaxial direction of the tire smaller than the second angle of the axiallymiddle portion, and the shoulder lateral grooves including a firstshoulder lateral groove and a second shoulder lateral groove, theaxially middle portion of the first shoulder lateral groove disposedaxially inwardly of the axially middle portion of the second shoulderlateral groove, the first shoulder lateral groove and the secondshoulder lateral groove alternately arranged in a circumferentialdirection of the tire, wherein the tread portion comprises a shoulderblock row that includes a plurality of shoulder blocks each divided byadjacent first and second shoulder lateral grooves between one of thetread edges and one of the shoulder main grooves, and wherein one of theshoulder blocks is provided with a circumferentially extendinglongitudinal sipe that extends from the axially outer portion of thefirst lateral groove to the middle portion of the second shoulderlateral groove.
 2. The tire according to claim 1, wherein the axiallyouter portion of the shoulder lateral groove has a groove widthincreasing toward axially outwardly of the tire.
 3. The tire accordingto claim 1, wherein the third angle of the second shoulder lateralgroove is smaller than the third angle of the first shoulder lateralgroove.
 4. The tire according to claim 1, wherein the axially middleportion of the second shoulder lateral groove has a circumferentiallength larger than that of the axially middle portion of the firstshoulder lateral groove.
 5. The tire according to claim 1, wherein oneof the axially middle portions of the shoulder lateral grooves has agroove width measured along the circumferential direction of the tire,and the groove width gradually increases toward the tread edge.
 6. Thetire according to claim 1, wherein the axially middle portions of theshoulder lateral grooves have groove widths measured along thecircumferential direction of the tire, and the groove widths graduallyincrease toward the tread edge.